The present invention relates to optical fiber communication systems, and more particularly to apparatus for remotely pumping active optical devices such as optical amplifiers and lasers distributed along an optical fiber communication path.
Optical fiber communication systems are well known. Such systems are enjoying increasing use in the telecommunications industry, in the cable television industry, and in local area networks used to couple personal computers and/or workstations together.
In the cable television industry, signal distribution via coaxial cable has dominated to date. Such systems are typically arranged in tree and branch networks, and require a large number of high bandwidth electrical amplifiers to amplify the program signals in the distribution path. In a coaxial cable system, on the order of 40 amplifiers may be required between the cable system headend and an individual subscriber's home.
Optical fiber distribution systems also require the amplification of the signal along the distribution path. Prior to the widespread availability of efficient optical amplifiers, many systems converted the optical signals into electrical signals for amplification by conventional electrical amplifiers. The amplified electrical signals were then reconverted to the optical domain, for further distribution along the optical communication path. The advent of reliable and low cost optical amplifiers has obviated the need to convert signals into the electrical domain for amplification. However, some types of optical amplifiers, such as rare earth doped optical fiber amplifiers, require a source of pump energy. In a rare earth doped optical fiber amplifier, for example, a dedicated pump laser is coupled to the doped fiber for exciting the active medium (rare earth element) within the amplifier. At the same time, a communication signal is passed through the doped fiber. The pumped fiber exhibits gain at the wavelength of the communication signal, providing the desired amplification.
One disadvantage of the use of pumped optical amplifiers is that electrical energy must be provided at the amplifier location in order to operate the pump laser. This requires the distribution plant to include expensive power supplies and an associated power distribution system similar to that which was required in prior art coaxial cable systems and fiber systems using electrical amplification. The need for remote power supplies increases the cost and decreases the reliability of the system.
It would be advantageous to provide an optical fiber communication system that provides the necessary signal amplification or other active optical function along the signal distribution path without requiring electrical power at the site of each active optical component. It would be further advantageous to provide such a system that uses highly reliable and efficient, low cost active devices, such as optical amplifiers, along the optical communication path. The present invention provides apparatus for distributing signals over an optical fiber communication path which enjoys the aforementioned advantages.